1. Field of the Invention
The present invention relates to an image data output apparatus such as various CRT displays or printers and, more particularly, to an image data output apparatus having a plurality of fonts.
2. Description of the Prior Art
Most conventional image data output apparatuses such as a line printer or a character display have a single font.
However, in accordance with recent spread of high-precision displays, high-resolution non-impact printers and low-cost large-capacity read-only memories (ROMs), apparatuses outputting a plurality of fonts are increasing in number. Some of these image output apparatuses have such fonts at their output sides. Particularly, in high-performance wordprocessors, printing or displaying by a plurality of fonts becomes increasingly important. In addition to this, it is expected that the number of kinds of fonts will increase.
It should be noted that "font" means a set of character patterns having the same attributes such as a character set (code or the like), a type face, a type size, a type inclination, a type thickness or the like. Note that characters here include symbols, figures and the like.
Conventionally, when a font select command is supplied to an output apparatus having such a pluraity of fonts, an identification label of a font or an attribute of the font is designated. In this case, if the output apparatus has the font which coincides with the designated label or attribute, the output apparatus selects the designated font. If the designated font does not exist, the output apparatus stops its output operation or provides an error display. Thus, a state wherein the designated font does not exist has been treated as an abnormal state. In this case, a host system as a data source must be able to recognize a font mounting state of the output apparatus.
When a small and fixed number of fonts is mounted in an output device, such a conventional apparatus can meet this requirement. However, it is difficult for a host system side to recognize a font mounting state of an output apparatus having a plurality of fonts. Particularly, in an output apparatus in which the font mounting states are different for every user, a load to a host system side becomes considerable. For example, assume that an output apparatus having a font "A" and an output apparatus which does not have the font "A", but has a font "A'" having attributes near to those of the font "A" are provided. When a host system supplies data to the respective apparatuses, it must generate a font "A" select command and a font "A'" select command, respectively. In other words, since the host system completely depends upon the font mounting state of the output apparatus, it can only generate a command corresponding to it. Therefore, the host system cannot generate a command such as "A-like font".